Frequency/timing of monitoring whilst on lithium therapy

• ideal sampling time is twelve hours after the last dose of drug (1). In practice, an interval of 10-14 hours between the last dose and the blood sample is acceptable as long as the delay after the dose is noted and the interval is the same at each measurement (1).
• monitoring should be weekly until the serum level is stable (in general, after 2 weeks). Then monitoring should be at 1- or 2- month intervals for the first 6 months of lithium therapy
  
  
• monitoring interval can then be extended if lithium levels are stable and adherence to therapy is good - NICE suggests that monitoring of serum lithium levels should normally occur every 3 months (2,3)
  • the person's plasma lithium level shoule be measured every 3 months for the first year
  • after the first year, measure plasma lithium levels every 6 months, or every 3 months for people in any of the following groups:
    • older people
    • people taking drugs that interact with lithium
    • people who are at risk of impaired renal or thyroid function, raised calcium levels or other complications
    • people who have poor symptom control
    • people with poor adherence
    • people whose last plasma lithium level was 0.8 mmol per litre or higher
      
      
• lithium levels should be checked immediately if there is any suggestion of relapse or lithium toxicity
  
  
• serum creatinine, calcium (long-term lithium treatment is associated with persistent hyperparathyroidism and hypercalcaemia) and thyroid function need to be regularly checked (1)
  • thyroid and renal function tests should be undertaken every 6 months, and more often if there is evidence of impaired renal function

Notes (2,3):

• undertake more frequent monitoring of lithium levels if there is evidence of clinical deterioration, abnormal results, a change in sodium intake, or symptoms suggesting abnormal renal or thyroid function such as unexplained fatigue, or other risk factors, for example, if the patient is starting medication such as ACE inhibitors, non-steroidal anti-inflammatory drugs, or diuretics
• closer monitoring of lithium dose and blood serum levels is required if urea and creatinine levels become elevated
  • decision whether to continue lithium depends on clinical efficacy, and degree of renal impairment; prescribers should seek specialist advice in this situation
• monitor for symptoms of neurotoxicity, including paraesthesia, ataxia, tremor and cognitive impairment, which can occur at therapeutic levels
• monitor weight, especially in patients with rapid weight gain
  • NICE suggests (3)
    • every 6 months
      • measure the person's weight or BMI and arrange tests for urea and electrolytes including calcium, estimated glomerular filtration rate (eGFR) and thyroid function
      • increase frequency of monitoring if there is evidence of impaired renal or thyroid function, raised calcium levels or an increase in mood symptoms that might be related to impaired thyroid function
      • monitor lithium dose and plasma lithium levels more frequently if urea levels and creatinine levels become elevated, or eGFR falls over 2 or more tests, and assess the rate of deterioration of renal function
• warn people taking lithium not to take over-the-counter non-steroidal anti-inflammatory drugs and avoid prescribing these drugs for people with bipolar disorder if possible; if they are prescribed, this should be on a regular (not p.r.n.) basis and the person should be monitored monthly until a stable lithium level is reached and then every 3 months

Reference:

1. Drug and Therapeutics Bulletin 1999;37 (3): 22-24.
2. NICE (July 2006). Bipolar disorder.
3. NICE (April 2018). Bipolar disorder.